The field of the present invention is vehicle engine brakes and the control thereof.
Engine brakes are typically valves operatively positioned in exhaust systems of internal combustion engines for greatly impeding the flow of exhaust gases from the engine. Such devices are commonly employed on diesel engines which are not throttled. They may be used on throttled gasoline engines as well. In principle, the engine brake resists exhaust flow from the engine under conditions when the engine is running by power derived from the wheels through the drive train rather than by internal combustion. Under such circumstances, the engine operates as a piston pump, drawing air through the intake and forcing it through the exhaust. By restricting exhaust flow, greater pressures are experienced within the engine cylinders to create retarding or braking power.
Such engine brakes are located within the exhaust train downstream of the engine exhaust manifold. Butterfly valves with restricted holes therethrough or measured clearance about the periphery are pivotally mounted within the exhaust train. Most commonly, the vehicle operator has access to a switch within the vehicle cab to either activate or deactivate the valve. The valve is often controlled by one of a hydraulic cylinder, a pneumatic vacuum cylinder and an electric actuator. Links typically convert linear actuation to valve rotation. Recent such brakes offer the operator a choice of valve positions controlled through a selector within the cab.
Engine brakes are understood to be most prevalent on diesel engines. Such brakes are less effective on gasoline engines because such engines are throttled. With engine power off, modern gasoline internal combustion engines can include electronic control for disabling the fuel injection system. In addition, the throttle valve or valves within the engine intake are closed when power is not applied. Vacuum is generated in the intake with the engine in this mode. With the throttle valve on the engine intake closed, the ability of the valve in an engine brake to develop pressure within the engine is severely compromised. Consequently, with the fuel off and the engine brake on, it has been found advantageous to open the throttle valve or valves in order that the engine brake can be fully enabled.
As the engine brake is designed to substantially increase pressure within the exhaust manifold and, in turn, the engine itself when the power is off, such brakes typically are deactivated with application of the accelerator pedal. With initiation of internal combustion, significantly more exhaust flow is created which, without the automatic shutoff, would result in damaging overpressure and heat.
With the need to disable the exhaust valve upon application of power to the engine and with the limited control capability on the valves of such engine brakes, a desired speed range is often difficult to maintain unless the downgrade is sufficiently steep that both the engine brake and the wheel brakes are needed to prevent acceleration. In such a circumstance, the wheel brakes modulate the braking to maintain a desired speed. The more current engine brake designs have multiple settings selected by the operator from the cab. The multiple settings offer finite additional control. Even so, the settings are not responsive to vehicle conditions.
The present invention is directed to an engine braking system including both apparatus and method. The invention contemplates modulation of vanes in the turbine wheel inlet of a variable inlet turbine on a turbocharger system responsive to engine conditions.
In a first separate aspect of the present invention, an engine brake for a vehicle drive system includes a vehicle speed sensor, variable inlet nozzle vanes in the turbine wheel inlet of the variable inlet turbine and a controller defining an inlet open position, an inlet closed position and intermediate positions therebetween. The position of the controller is determined by conditions of the vehicle drive system including a speed signal from the vehicle speed sensor. Through such a system, target conditions can be presented which the controller operates to approach. Consequently, the overall braking system is more flexible in achieving selected speeds.
In a second separate aspect of the present invention, an engine brake for a vehicle drive system includes a vehicle speed sensor, variable inlet nozzle vanes and a controller defining an inlet open position, an inlet closed position and intermediate positions therebetween. The position of the controller is determined by conditions of the vehicle drive system including the vehicle speed and the magnitude of acceleration. Through such a system, response to target conditions which the controller operates to approach can vary depending upon need. Consequently, the overall braking system is more flexible and responsive in achieving selected speeds.
In a third separate aspect of the present invention, the features of the first or second separate aspects further include an internal combustion engine with an exhaust system as part of a drive system. In the case of a gasoline internal combustion engine with an intake throttle valve, the controller further includes a throttle valve disabling signal to the throttle valve. For diesel engines, such a disabling signal is unnecessary.
In a fourth separate aspect of the present invention, an engine brake for a vehicle drive system which includes an internal combustion engine, an exhaust system and an automatic transmission includes a vehicle speed sensor, variable inlet nozzle vanes and a controller in communication with the speed sensor and coupled with the variable inlet nozzle vanes. The controller modulates the inlet based upon parameters of the vehicle such as vehicle speed, vehicle acceleration and exhaust manifold back pressure. The controller includes output shift signals in communication with the automatic transmission. The controller is able to employ both higher and lower gearing to assist in engine braking control. Control can additionally be extended by locking and unlocking a torque converter.
In a fifth separate aspect of the present invention, an engine brake for a vehicle drive system includes a exhaust manifold pressure sensor, variable inlet nozzle vanes and a controller defining an inlet open position, an inlet fully shut position and intermediate positions therebetween. The position of the controller is determined by conditions of the exhaust manifold pressure. Through such a system, increased braking efficiency can be achieved at low engine speeds.
In a sixth separate aspect of the present invention, a method of braking contemplates the selection of a vehicle speed value, a sensing of the vehicle speed and a comparison between the two. Variable inlet nozzle vanes are modulated responsive to the difference between the vehicle speed value and the vehicle speed.
In a seventh separate aspect of the present invention, the features of the sixth separate aspect further include the calculation of the rate of change of the vehicle speed. More or less aggressive changes in any of the inlet modulation, transmission gear selection and torque converter engagement can be employed based on the rate of change of the vehicle speed.
In an eighth separate aspect of the present invention, a method of braking contemplates the sensing of the exhaust manifold pressure. Exhaust flow is modulated responsive to the exhaust manifold pressure by controlling variable inlet nozzle vanes. Greater braking efficiency is achieved at low engine speeds.
In a ninth separate aspect of the present invention, combinations of any of the foregoing aspects are contemplated.
Accordingly, it is an object of the present invention to provide improved engine brake systems offering greater flexibility and control. Other and further objects and advantages will appear hereinafter.